Editing Osmium (section)

=== Isotopes ===
{{Main|Isotopes of osmium}}
Osmium has seven naturally occurring [[isotope]]s, five of which are stable: {{chem|187|Os}}, {{chem|188|Os}}, {{chem|189|Os}}, {{chem|190|Os}}, and (most abundant) {{chem|192|Os}}. At least 37 artificial radioisotopes and 20 [[nuclear isomer]]s exist, with mass numbers ranging from 160 to 203; the most stable of these is {{chem|194|Os}} with a half-life of 6 years.<ref name="nubase">{{NUBASE2020}}</ref>

{{chem|186|Os}} undergoes [[alpha decay]] with such a long [[half-life]] {{val|2.0e15|1.1}} years, approximately {{val|140000}} times the [[age of the universe]], that for practical purposes it can be considered stable. {{chem|184|Os}} is also known to undergo alpha decay with a half-life of {{val|1.12e13|0.23}} years.<ref name="184Os"/> Alpha decay is predicted for all the other naturally occurring isotopes, but this has never been observed, presumably due to very long half-lives. It is predicted that {{chem|184|Os}} and {{chem|192|Os}} can undergo [[double beta decay]], but this radioactivity has not been observed yet.<ref name="nubase"/>

<sup>189</sup>Os has a spin of 5/2 but <sup>187</sup>Os has a nuclear spin 1/2. Its low natural abundance (1.64%) and low nuclear magnetic moment means that it is one of the most difficult natural abundance isotopes for [[NMR spectroscopy]].<ref>{{cite journal|doi=10.1021/om960053i |title=<sup>187</sup>Os NMR Study of (η<sup>6</sup>-Arene)osmium(II) Complexes: Separation of Electronic and Steric Ligand Effects |date=1996 |last1=Bell |first1=Andrew G. |last2=Koźmiński |first2=Wiktor |last3=Linden |first3=Anthony |last4=von Philipsborn |first4=Wolfgang |journal=Organometallics |volume=15 |issue=14 |pages=3124–3135 }}</ref>

{{chem|187|Os}} is the descendant of {{chem|187|[[rhenium|Re]]}} (half-life {{val|4.56|e=10|u=years}}) and is used extensively in dating terrestrial as well as [[meteorite|meteoric]] [[rock (geology)|rocks]] (see ''[[Rhenium–osmium dating]]''). It has also been used to measure the intensity of continental weathering over geologic time and to fix minimum ages for stabilization of the [[Earth's mantle|mantle]] roots of continental [[craton]]s. This decay is a reason why rhenium-rich minerals are abnormally rich in {{chem|187|Os}}.<ref>{{cite journal|first=Józef|last=Dąbek|author2=Halas, Stanislaw|title=Physical Foundations of Rhenium-Osmium Method – A Review|journal=Geochronometria|volume=27|date=2007|issue=1 |doi=10.2478/v10003-007-0011-4|pages=23–26|bibcode=2007Gchrm..27...23D |doi-access=free}}</ref> However, the most notable application of osmium isotopes in geology has been in conjunction with the abundance of iridium, to characterise the layer of [[shocked quartz]] along the [[Cretaceous–Paleogene boundary]] that marks the extinction of the non-avian [[dinosaur]]s 65 million years ago.<ref name="Alvarez">{{cite journal|title=Extraterrestrial cause for the Cretaceous–Tertiary extinction|author=Alvarez, L. W.|author-link=Luis Walter Alvarez|author2=Alvarez, W.|author3=Asaro, F.|author4=Michel, H. V.|date=1980|journal=Science|volume=208|issue=4448|pages=1095–1108|doi=10.1126/science.208.4448.1095|pmid=17783054|bibcode=1980Sci...208.1095A|url=http://earthscience.rice.edu/wp-content/uploads/2015/11/Alvarez_K-Timpact_Science80.pdf|citeseerx=10.1.1.126.8496|s2cid=16017767|access-date=November 2, 2017|archive-date=May 21, 2023|archive-url=https://web.archive.org/web/20230521231012/https://earthscience.rice.edu/wp-content/uploads/2015/11/Alvarez_K-Timpact_Science80.pdf|url-status=live}}</ref>